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Morphy

...games, pawns and knights played minor roles. Pawns were often sacrificed so that the queen, rooks, and bishops could join the attack as soon as possible. The first priority for Morphy was the
initiative, the ability to force matters. Superior development in a position with few centre pawns conferred the
initiative on one player. In the games of lesser players the
initiative might pass...

Soviet chess theory

The Soviets valued the
initiative—the ability to force matters—more than most positional considerations. While the Hypermoderns and Lasker often challenged their opponents to make the first aggressive moves, the Soviets regarded the
initiative as vitally important. When defending, they rejected the solid if passive approach of Steinitz and Tarrasch and tried to generate a...